Positional selectivity in the interaction of toluene with nitronium ion
Three alternative theoretical approaches – electrostatic potentials at the ring carbon atoms, Hirshfeld charges, and electrophile affinities – are employed in predicting the positional selectivity for the nitration of toluene with nitronium ion in dichloromethane medium. The theoretical estimates are compared with recent experimental data of Nieves-Quinones and Singleton. The computed electrostatic potential values at the ring carbon nuclei and the respective Hirshfeld charges predict excellently the regioselectivity of the reaction. The electrophile affinity approach, based on estimated energies of formation of the σ-complex intermediates for the ortho, meta, para, and ipso positions in the ring, also provides reasonable theoretical predictions of reactivity. The mechanism of the nitration reaction is also discussed.